How do you site in your chair?
 

I know this sounds like an odd question but being a tall lady it's hard for me to sit with my legs under the desk for up to 15 hours a day. I'm constantly moving and changing my sitting position. Sometimes I tuck a leg underneath myself and sometimes I have a foot in my chair with my knee bent in front of me. The point of my question is my knees hurt like hell and I was wondering if some super genius that sits at his computer as much as I do has figured out a comfy way to sit without ruining his knees.